Editorial pubs.acs.org/JAFC
ACS Select on Nanotechnology in Food and Agriculture: A Perspective on Implications and Applications
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science for food safety Farahi and coauthors concluded that nanotechnology is clearly a big part of the future in sensor science because of advantages such as “...greater effective functionalized sensing surface area in a compact form...high sensitivity due to their small size...unique optical and electrical properties...fast response due to high elastic (spring) constants; and...highly localized detection of entities of comparable size”. These advantages go hand-in-hand with challenges; sensors have been laboratory-tested but few field tests, which would gauge progress toward overcoming these challenges, have been conducted.3 Selectivity and sensitivity make them potentially transformative. In a nanoparticle-based immunoassay, where antibodies are immobilized on magnetic beads, Zhang et al. are able to monitor for marine toxins in seafood down to a concentration of picograms per milliliter.4 Apak et al. provide a good example of selective nanoscale sensors by binding oxidant sensitive dyes to the surface of nanoscale TiO2 and determining the catechin content of various types of tea (catechin molecules bestow teas with a majority of their beneficial health effects).5 Zhang et al. have developed a time- and temperature-sensitive indicator for perishable products using gold and silver plasmonic nanocrystals that can be tuned to change color from red to green on the basis of the temperatures they are exposed to and the time since the food has been packaged.6 It is envisioned by scholars and stakeholders that the convergence between nanotechnology, biotechnology, and agricultural and environmental sciences will lead to revolutionary advances in the next 5−10 years. Some applications on the horizon may include, but are not limited to • development of nanotechnology-based foods with lower calories and less fat, salt, and sugar while retaining flavor and texture; • nanoscale vehicles for effective delivery of micronutrients and sensitive bioactives; • re-engineering of crops, animals, and microbes at the genetic and cellular level; • nanobiosensors for detection of pathogens, toxins, and bacteria in foods; • identification systems for tracking animal and plant materials from origination to consumption; • integrated systems for sensing, monitoring, and active response intervention for plant and animal production; • smart field systems to detect, locate, report, and direct application of water; • precision and controlled release of fertilizers and pesticides; • development of plants that exhibit drought resistance and tolerance to salt and excess moisture; and • nanoscale films for food packaging and contact materials that extend shelf life, retain quality, and reduce cooling requirements.
owder that makes doughnuts white may have, until recently, been the most well-known food containing manufactured nanoscale particles. This may be rapidly changing. The growing ability to create and manipulate on the nanoscale indicates it is only a matter of time before more engineered nanomaterials (ENMs) are found on our farms, in our grocery stores, and on our plates. What we do not know yet is what forms these technologies will take. This causes simultaneous excitement for potentially better and healthier products and concern due to multifaceted new properties yet to be fully understood by the scientific community. The budding nature of the field is reflected in this ACS Select on Nanotechnology in Food and Agriculture: Implications and Applications. As recently published papers from six ACS journals were being selected, it quickly became apparent that much work was being conducted on the implications of these ENMs. Papers focused on consequences of widespread use by examining effects on the environment, agriculture, and plants, and humans through direct consumption. However, work has also begun in the area of application of nanoscale science to food and agriculture. New nanosensors for improving food quality and safety and packaging techniques that will change the way food is stored and delivered have been the primary application foci among authors featured in this Select.
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APPLICATIONS Potential applications of nanoscale sciences to food and agriculture are limited only by the imagination. Papers in this ACS Select demonstrate that the majority of the work is being done on nanoscale biomaterials, packaging, and sensors to enhance the shelf life of foods and more carefully detect when undesirable compounds are present in food. Encapsulation of active compounds in packaging in nanoscale electrospun fibers is an attractive option for enhancing the shelf life of packaged foods. Kayaci et al. describe their successful efforts to lend more stability to the eugenol molecule, a popular preservative choice in the food industry due to its natural origins and extraction from plants, as well as antibacterial, antifungal, and antioxidant activities.1 Eugenol is quite susceptible to degradation by oxygen, light, and heat, but encapsulation in cyclodextrin inclusion complexes is shown to aid the thermal stability of the preservative. The controlled/ slow release of active ingredients encapsulated is another advantage for many applications of delivery of valuable payloads. Nanocellulose is a biomaterial that is seeing growing use in food packaging and other applications. Although the end product is biodegradable and biocompatible, Li et al. perform a life cycle assessment examining the environmental impacts of fabricating this nanoscale form of cellulose.2 The environmental footprint increases significantly when compared with a standard procedure for extraction of raw cellulose materials, but is much less than that of the production of carbon nanotubes. Nanoscale sensors will be extremely important tools for food quality and safety in the near future. In a review of sensor © 2014 American Chemical Society
Published: January 30, 2014 1209
dx.doi.org/10.1021/jf5002588 | J. Agric. Food Chem. 2014, 62, 1209−1212
Journal of Agricultural and Food Chemistry
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Editorial
IMPLICATIONS Applications for the future of food and agriculture are exciting to consider, but a look at the current literature reveals a precautionary note struck by researchers. Implications involve risks for both the environment and organisms within that environment (including humans). Researchers in this area are studying hazards by examining the harm done when nanomaterials reach the nanobio interface. They are also studying exposure by determining how ENMs transport in the environment, how ENMs might accumulate, the types and quantities of ENMs we are currently exposed to through products we already consume, and what the fate of those materials might be in our digestive tracts. Researchers have asked the following questions: How do we measure the ecotoxicity of these emerging technologies? How do we make these technologies safe/ How do we make these technologies sustainable? Reviews of econanotoxicology found in this ACS Select describe the challenge of quantifying the hazards of ENMs that vary in size, shape, surface area, and coating to a wide variety of organisms ranging over several trophic levels. The researchers’ goal is to understand how to make these ENMs more sustainable before full-scale release to the environment. Zhu et al. summarize the current understanding of the cellular uptake, intracellular fate, and transformation as affected by the physicochemical properties of ENMs and suggest that the advancement of research in this field along with better analytical capabilities and in silico simulation may lead to safe-by-design ENMs.7 Mauer-Jones et al. discuss three grand challenges for chemists involved in econanotoxicity work: functional level toxicity assessment; detecting ENMs and distinguishing them from the background particles; and particle characterization in complex environments.8 In addition, Kahru et al. review the econanotoxicological research done on aquatic species concluding that although computational methods such as quantitative structure−activity relationships (QSARs) are attractive for solving the problem, too many material types and too many organism types make these relationships difficult to apply due to lack of quality experimental data.9 As a new approach to this problem, in their review Holden et al. propose high-throughput screening integrated with dynamic energy budget models.10 Whether nanoparticles are intentionally applied during agricultural processes or they are present as contaminants, it is important to understand what effects they will have on plants and more specifically plants grown for food. To investigate this question, Dimpka et al. amended sand with silver nanoparticles and grew wheat plants, disrupting the growth of shoots and roots in a dose-dependent manner.11 Ma et al. performed a similar study utilizing Arabidopsis thaliana and either CeO2 or In2O3 nanoparticles. The physiological and molecular responses were different between the two particles, with CeO2 inhibiting root and shoot growth in a dose-dependent manner (concentrations ranged from 0 to 2000 ppm).12 Reviewing the direct and indirect effects of many different types of ENMs on algae, a species at the bottom of the ocean food web, Quigg et al. noted that the presence of exopolymeric substances produced by the organisms play a major role in the toxicity demonstrated by the particles.13 In addition, they discuss how little is known about the biological uptake mechanisms and toxicity of nanoparticles in general.
Nanomaterial fate in the environment is discussed by Bately et al., who suggest that currently there is low risk of exposure, that the concentrations reaching the nanobio interface will be very low, and that work needs to be continued on studying toxicity under real environmental conditions to define no-effect concentrations.14 Although environmental concentrations may be low, there is a risk that these materials will accumulate in certain receptors and compartments, resulting in much higher concentrations. Three studies found in this ACS Select examine the potential for bioaccumulation. Metallic and metal oxide ENMs can be measured in samples taken from plants using X-ray fluorescence; using this technique, Hernandez-Viezcas and coauthors examined whether soil contaminated with zinc oxide and cerium oxide ENMs results in a bioaccumulation of particles in soybean crops.15 Their results indicate that changing particle types will alter how they interact with the plant and whether or not they will accumulate. Using a transmission electron microscopy approach, Wang et al. demonstrated that copper oxides will bioaccumulate in maize plants translocating from the roots to the shoots and back again.16 Another important process that is just beginning to be studied is trophic transfer, the movement of pollutants up the food chain. A simulated transfer of soil contaminated with gold nanoparticles to earthworms and subsequently to bullfrogs undertaken by Unrine and coauthors showed that this transfer does occur, but concentrations decrease by 2 orders of magnitude with each step.17 Humans are exposed to ENMs through food consumption. What is the current level of exposure? How are we processing them once they enter our digestive systems? Two research papers highlighted in this ACS Select ask these questions by examining the titanium dioxide found in food products already on the market and performing an in vitro study designed to simulate digestion of products containing a silica nanoparticle additive. Analysis by Weir et al. showed that children may have the highest exposure level to titanium dioxide in food because candy products contain a relatively high concentration of the material.18 When silica ENMs enter our digestive systems, Peters and coauthors showed nanoscale particles could appear in the gut epithelium after digestion in the stomach, cause for concern and further research.19 Scientists agree that although nanoscale technology is promising for food and agriculture, the development must be done in a sustainable manner. Governments, through existing regulations, will play a large part of this development. It was through this lens that Bergeson examined if existing laws are sufficient to govern ENM development in a sustainable manner; because the state of knowledge is still playing catchup, development entities involved in regulation must adapt new procedures to promote sustainability.20 Despite the fact that the environmental health and safety of some ENMs have been extensively studied in the past decade, as evident in this issue of ACS Select, knowledge gaps still widely exist in many aspects including • measurement and metrology of ENMs in complex matrixes; • environmental fates and transformation of currently known ENMs and ever-increasing number of new ENMs; • nanobio interface between ENMs with human body and ecosystem species; 1210
dx.doi.org/10.1021/jf5002588 | J. Agric. Food Chem. 2014, 62, 1209−1212
Journal of Agricultural and Food Chemistry
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• exposure and full life cycle assessment; • risk assessment and management of diverse uses of ENMs; • safety by design; and • sustainable nanomaterials and nanomanufacturing. Predictive models for the effects of nanomaterials on cells/ living tissues have shown promise but still have a long way to go to be fully useful. High-throughput and high-content screening approaches using model biological species may be used to more effectively reveal mechanisms of nanomaterials safety. Nanoinformatics for nanomaterials design, data integration, and communication is an emerging field of study. In addition, risk governance of nanotechnology for societal benefit is still in a formative stage.
Editorial
AUTHOR INFORMATION
Corresponding Author
*(H.C.) E-mail:
[email protected]. Notes
Views expressed in this editorial are those of the authors and not necessarily the views of the ACS, the U.S. government, or the National Institute of Food and Agriculture (NIFA) of the U.S. Department of Agriculture (USDA).
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ACKNOWLEDGMENTS We thank the teams from Accounts of Chemical Research, ACS Nano, Analytical Chemistry, ACS Sustainable Chemistry & Engineering, Environmental Science & Technology, and Journal of Agricultural and Food Chemistry for helping support this ACS Select by identifying content for inclusion.
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CONCLUSION Nanoscale science is an exciting scientific frontier focusing on the length scale of approximately 1−100 nm. Advancement of analytical instrumentation has tremendously enhanced our ability to observe physical and biological worlds at the nanoscale and lead to creation of numerous new materials and functions at this length scale. Emergence of novel concepts and discovery of unexpected properties stimulate new approaches in traditional scientific disciplines. Combining these developments with the need to feed a predicted 9 billion people by 2050 establishes the intersection of nanotechnology, food, and agriculture as a research priority in the coming years. Many applications of nanotechnology have been explored across the whole spectrum of national economic sectors, including agriculture, food, forest, and the environment, with demonstrated societal benefits. In the vast literature of nanoscale science, engineering, and technology, the majority is of discovery and application nature, whereas a relatively small portion, one estimate at
